Creating and updating Symfony projects much faster

A few years ago, we introduced the Symfony Installer as the fastest way to
create new Symfony projects. While Composer took up to several minutes to create
a new project, Symfony Installer did the same in less than ten seconds.

The trick was that the installer downloaded a ZIP archive with all the
dependencies required by the specific Symfony version you were installing, so
it was not necessary that Composer resolved the project dependencies.

However, with the release of Symfony 4 we deprecated the Symfony Installer in
favor of Composer, because we wanted to use standard development tools as much
as possible. Sadly this made creating new Symfony projects slower and, in some
cases, it triggered "out of memory" exceptions while Composer was resolving the
dependencies.

During the past months we've worked hard to improve the performance of
Symfony Flex, the package used to create and manage Symfony apps. A few days
ago, we made the two biggest improvements ever:

The two skeletons used to create new Symfony projects, symfony/skeleton (for
small apps, APIs, microservices, etc.) and symfony/website-skeleton (for
traditional web applications) now include a composer.lock file to avoid
Composer's dependency resolving (see symfony/skeleton #66 and symfony/web-skeleton #11).
An automatic process ensures that those composer.lock files are updated
whenever a dependency has a new version.

Symfony Flex removes all the legacy Composer tags from all Symfony components
before creating the project. This removes hundreds of unused tags and saves
Composer hundreds of thousands of unnecessary checks.

Thanks to these changes, creating new Symfony projects is between 60% and 90%
faster and updating existing projects is up to 50% faster. Actual results may
vary depending on your Composer cache, the size of your project and the speed of
your Internet connection.